View an animation from the Extreme ultraviolet Imaging Telescope (EIT).

At 4:51 p.m. EDT, on Monday, April 2, 2001, the sun unleashed the
biggest solar flare ever recorded, as observed by the Solar and
Heliospheric Observatory (SOHO) satellite. The flare was definitely
more powerful than the famous solar flare on March 6, 1989, which was
related to the disruption of power grids in Canada. This recent
explosion from the active region near the sun's northwest limb hurled a
coronal mass ejection into space at a whopping speed of roughly 7.2
million kilometers per hour. Luckily, the flare was not aimed directly
towards Earth.

Solar flares, among the solar system's mightiest eruptions, are
tremendous explosions in the atmosphere of the Sun capable of releasing
as much energy as a billion megatons of TNT. Caused by the sudden
release of magnetic energy, in just a few seconds flares can accelerate
solar particles to very high velocities, almost to the speed of light,
and heat solar material to tens of millions of degrees.

Solar ejections are often associated with flares and sometimes occur
shortly after the flare explosion. Coronal mass ejections are clouds of
electrified, magnetic gas weighing billions of tons ejected from the Sun
and hurled into space with speeds ranging from 12 to 1,250 miles per
second. Depending on the orientation of the magnetic fields carried by
the ejection cloud, Earth-directed coronal mass ejections cause magnetic
storms by interacting with the Earth's magnetic field, distorting its
shape, and accelerating electrically charged particles (electrons and
atomic nuclei) trapped within.

Severe solar weather is often heralded by dramatic auroral displays,
northern and southern lights, and magnetic storms that occasionally
affect satellites, radio communications and power systems. The flare and
solar ejection has also generated a storm of high-velocity particles,
and the number of particles with ten million electron-volts of energy in
the space near Earth is now 10,000 times greater than normal. The
increase of particles at this energy level still poses no appreciable
hazard to air travelers, astronauts or satellites, and the NOAA SEC
rates this radiation storm as a moderate S2 to S3, on a scale that goes
to S5.

Monday's solar flare produced an R4 radio blackout on the sunlit side of
the Earth. An R4 blackout, rated by the NOAA SEC, is second to the most
severe R5 classification. The classification measures the disruption in
radio communications. X-ray and ultraviolet light from the flare changed
the structure of the Earth's electrically charged upper atmosphere
(ionosphere). This affected radio communication frequencies that either
pass through the ionosphere to satellites or are reflected by it to
traverse the globe.

The SOHO mission is being conducted collaboratively between the European
Space Agency and NASA.